In lubrication systems, where a lubricant is circulated in order to provide lubrication, e.g. for a moving part, it is undesirable that contaminants, e.g. in the form of debris, are present in the lubricant, since this may potentially lead to damage of the moving part. More important, contaminants may, e.g., originate from the moving part being lubricated, and as a consequence of the movements of the moving part, and in this case the presence of contaminants in the lubricant is an indication that a moving part has already suffered some damage, e.g. in the form of white structure flacking or tooth fracture. In the case that the moving part is made from a magnetizable material, such as iron, nickel, cobalt, or alloys containing iron, nickel or cobalt, the contaminants will also be magnetizable. As an alternative, the magnetizable material may be rare earth metal.
Thus, it is desirable to be able to detect the presence of contaminants, such as magnetizable contaminants, in a lubricant, in order to detect if the moving part being lubricated has suffered some damage, and in order to prevent that the moving part is damaged further. This has previously been obtained by means of magnetic sensors.
US 2013/0332045 A1 discloses a system and a method for detecting a spall in an engine by means of an oil debris sensor. A processor may be configured to increment a counter when the oil debris sensor detects a particle over a predetermined size, and to increment the counter when a mass of a plurality of particles under the predetermined size exceeds a predetermined mass threshold. The processor may analyse data from the sensor to determine when a change in an electromagnetic field has occurred, indicating a debris article.
WO 2007/088015 A1 discloses an apparatus, in particular an inductive particle counter, for detecting particles in a fluid flow and associated cooling and/or lubricating system. The apparatus has at least one field coil for generating a magnetic field, which covers at least sections of the fluid flow, and a sensor coil which can be connected to an evaluation device which can be used to detect the presence of a particle in the fluid flow from the signal induced in the sensor coil.
The systems and methods disclosed in US 2013/0332045 A1 and WO 2007/088015 A1 rely on relatively complicated approaches for detecting the presence of contaminants in a lubricant flow.